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Conficker botnet stirs to distribute update payload

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The Conficker superworm is stirring, with the spread of a new variant that spreads across P2P and drops a payload. It is thought to update machines infected by earlier strains of the worm.

Conficker-E (the latest variant) offers potential clues on the origins of the worm, because of possible links to other malware. Trend Micro reports that the new Downadup/Conficker variant is talking to servers associated with the Waledac family of malware, in order to download further unwanted items.

Waledec, in turn, is suspected as the latest item of malware from the gang behind the Storm botnet, sparking speculation that all three strains of botnet client are the work of the same cybercriminal gang.

A preliminary analysis by Symantec suggests that PCs infected by earlier variants are getting updates.

On April 8, 2009 we discovered a new sample that is a slightly modified version of the original W32.Downadup worm. The worm previously updated its functionality with the .C variant which installed on top of the .B variant infections, and we are now seeing the same type of update happening on top of the .A variant infections.

This new sample reintroduces the MS08-067 exploit vector, which was removed in the .C variant. It includes previously unseen self-removal functionality to remove itself from the infected host on May 3, 2009. The new sample includes a slightly different list of URLs used to obtain the IP address of the infected host and also reaches out to a new list of high-profile domains to confirm the current date. When reaching out to these domains the threat is not exploiting any weakness nor downloading any code.

We have also observed a possible connection to W32.Waledac, one of the most active spam bots, and have some circumstantial evidence that the two may be linked with W32.Downadup.C distributing W32.Waledac. W32.Waledac steals sensitive information, turns computers into spam zombies, and establishes a back door remote access. Symantec products provide antivirus and IPS protection for Waledac.

This new sample does not appear to include any new infection vectors that might allow the threat to spread faster or onto new machines.

The latest variant of Conficker uses randomly generated ports between the ranges of 1024 and 10000 to communicate and propagate. Analysis of the malware, detected on Wednesday night, remains ongoing.

The malware components downloaded by the new version of Conficker may not themselves be anything new. Patrik Runald, chief security advisor at F-Secure, reports that his firm (at least) has detected these components since 30 December.

At the time of writing there's no evidence that access to the Conficker botnet is being used to send spam, launch denial of service attacks or any other nefarious activity normally associated with compromised PCs. ®